There is known a work machine including an exhaust gas purifying device that removes a nitrogen oxide (NOx) being discharged (cf. Patent Literature 1). Patent Literature 1 describes an exhaust gas after-treatment unit including: a selective catalytic reducing device; a reducing agent injection device that injects a reducing agent, such as a urea aqueous solution, into exhaust gas to be supplied to the selective catalytic reducing device; a cooling water supply pipe that guides cooling water to the injection device; and a cooling water return pipe for discharging the cooling water from the injection device.
The cooling water supply pipe and the cooling water return pipe each include a convection portion extending upward from a portion connected with the injection device along a connection pipe that guides the exhaust gas from the engine to the selective catalytic reducing device. In the technique described in Patent Literature 1, the convection portion is provided in each of the cooling water supply pipe and the cooling water return pipe, and after stopping of the engine, cooling water having increased in temperature due to absorption of heat from the injection device is convected in the convection portion to enable cooling of the injection device.